1. Field of Invention
The present invention relates to a method for production of seat belt webbing wherein the webbing is first woven using at least two synthetic yarns of different colors, of which at least one yarn is spun-dyed, and using weaves that are known per se. Furthermore, the invention is intended for seat belts containing such seat belt webbing.
2. Description of Related Art
A method of this type for production of seat belt webbing is known. DE-A-2902905, for example, describes a method for production of seat belt webbing patterned in bright colors for motor vehicles, aircraft, etc. in which the webbing is woven using at least two spun-dyed synthetic yarns of different colors, at least one yarn having a bright color, and using weaves that are known per se. The spun-dyed seat belt webbing of DE-A-2902905 is claimed to be distinguished by optimal color uniformity within the colors and patterns, optimal abrasion resistance, and resistance to heat and light. Furthermore, it is claimed to overcome the disadvantage of using yarn-dyed varieties or piece-dyed webbing, namely, the allegedly poor color-fastness of the dyes known at the time.
Seat belt webbing must satisfy stringent requirements in regard to usability, field of application and durability. In addition to having to meet strict specifications for abrasion resistance, resistance to light and heat, etc., seat belt webbing must be capable of being put in place and removed easily, and must always rest securely and comfortably on the wearer during use. Good retraction behavior of the seat belt webbing is particularly important for these last characteristics. In addition to a well adjusted retraction mechanism specially tailored to the specific application, the material properties of the webbing are particularly important here. Of these material properties, the surface of the webbing is of particular significance because its structure and properties decisively influence the retraction behavior.
Many attempts have been made to influence the surface properties of seat belt webbing in regard to retraction behavior. Particularly noteworthy in this respect is the thermofixing step, in which, following the weaving process, the yarns are for example subjected to hot-air treatment, resulting in a smoother surface of the webbing thus treated and therefore to improved retraction behavior.
Unfortunately, even these treatment steps have not proved to be effective in all cases. For example, the retraction behavior of seat belt webbing is not satisfactory precisely during use under extreme conditions such as very high, and particularly very low, temperatures. These problems are naturally most evident particularly when such seat belt webbing is being used after a lapse of time, for example when the seat belt is fastened in a vehicle that has been subjected to very high or low temperatures over a period of time. This is typically the case while starting in the morning following a cold night, or when the vehicle has been standing in strong sunlight for some time in the summer. The retraction behavior does normally improve subsequently under the influence of the heating or air-conditioning in the vehicle. However, this may not always be the case if, for example, the vehicle is driven for only a short time, or if suitable and effective air-conditioning equipment is not easily available.